Cryogenics: Did you hear about the cryogenicist who wanted his windows cleaned? He had Bose-Einstein condensation.

Physics: Did you hear about the French postdoc who went to work at Fermilab, but never went in because the sign over the door always said it was closed? (OK, OK, that one was more of a French joke than a physics joke! I'll make it up to you with two more!)